The present invention relates to a method for detecting the driving situation with respect to the yaw behavior of the vehicle, in which a desired value of the vehicle yaw angle rate .mu..sub.des is formed in a computer unit from measured values (vehicle speed, steering wheel angle), in which at least one sensor signal is supplied to the computer unit from which the actual value of the vehicle yaw angle rate .mu..sub.act is formed, the difference between the desired value of the yaw angle rate .mu..sub.des and the actual value of the yaw angle rate .mu..sub.act being formed in the computer unit, with the actual value of the yaw angle rate .mu..sub.act is subtracted from the desired value of the yaw angle rate .mu..sub.des, and at least one output signal, being generated in the computer unit from this difference. The output signal represents the detected driving situation with respect to the yaw behavior of the vehicle.
A method for detecting the driving situation with respect to the yaw behavior of a vehicle has already been disclosed in DE 36,25,392A1. The yaw angle rate .mu..sub.act of a vehicle is measured, for example, by a fiber-optic gyro. An alternative possibility for determining the actual value of the yaw angle rate .mu..sub.act is by deriving the yaw angle rate .mu..sub.act using at least one acceleration sensor, which measures the radial acceleration of the vehicle. Furthermore, a desired value of the yaw angle rate .mu..sub.act is derived from the measured speed of the vehicle in the longitudinal direction and the measured steering angle. In this case, a critical driving situation is derived when the actual value of the yaw angle rate .mu..sub.act deviates from the desired value of the yaw angle rate .mu..sub.des, i.e. when the actual behavior of the vehicle deviates from the desired behavior of the vehicle. This detected deviation of the actual behavior from the desired behavior of the vehicle is then used in order to minimize the deviation of the actual behavior of the vehicle from the desired behavior of the vehicle, in that an automatic intervention in the steering takes place and/or in that individual wheels of the vehicle are braked or accelerated in such that the deviation is minimized.
A so-called linear single-track model of a vehicle has been disclosed in other literature references (DE Book: Zomotor, Adam; Fahrwerktechnik [Running Gear Technology]: Fahrverhalten [Handling]; Publisher: Jornsen Reimpell; Wurzburg: Vogel, 1987; 1st Edition; ISBN 3-8023-0774-7, in particular pages 99-127), by way of which a vehicle yaw angle rate .mu..sub.act, which under some circumstances is self-adjusting, and is then used on the basis of this model as the desired value of the yaw angle rate .mu..sub.des, can be derived, for example, from measured values of the vehicle speed in the vehicle longitudinal direction and from the steering wheel angle or the steering angles of the wheels corresponding thereto.
An object of the present invention is to detect the driving situation with respect to the yaw behavior of the vehicle such that yaw reactions of the vehicle, which do not correspond with the desired behavior of the yaw reaction of the vehicle, can be detected as early as possible and with the greatest possible safety.
This object has been achieved according to the invention by forming the time derivative of the difference between the desired yaw angle rate and the actual yaw angle rate and generating an output signal as a function of the time derivative.
A further advantage of the present invention in comparison with the known prior art is that, as a result of the early detection of the driving situation with respect to the yaw behavior of the vehicle, unstable driving situations can be detected very early. Thus, vehicle driver can be warned very early of the possible occurrence of unstable driving situations and interventions into control devices of the vehicle can take place very early in order to be able to prevent unstable driving situations before their occurrence.
The vehicle longitudinal speed and the steering wheel angle or the steering angle of the wheels are detected by suitable sensors. These sensor signals can then be supplied to a computer unit in which a vehicle yaw angle rate .mu..sub.des, desired by the vehicle driver, can be determined as the desired value of the yaw angle rate .mu..sub.des from these variables, for example, in accordance with the aforementioned linear single-track model. The driving situation with respect to the yaw behavior is then detected in the computer unit in that the actual value of the yaw angle rate .mu..sub.act is compared with the desired value determined. In this case, not only the magnitude of the difference of the actual value of the yaw angle rate .mu..sub.act from the desired value .mu..sub.des is considered, but also the mathematical sign of this difference and the time derivative of this difference. A particularly early detection of the possible occurrence of critical driving situations is possible especially as a result of considering the time derivative, so that the vehicle driver can then be warned before the occurrence of these critical driving situations. It is likewise then also conceivable to carry out an intervention, for example, into the steering of the vehicle or into the braking of the individual wheels even before the occurrence of this critical driving situation, such that the tendency towards a difference between the actual value of the yaw angle rate .mu..sub.act and the desired value of the yaw angle rate .mu..sub.des is reduced even before a critical driving situation is reached.
Instead of determining the desired value of the yaw angle rate .mu..sub.des by the linear single-track model, it is likewise possible to determine this desired value from a performance graph measured once.